3 month old keeps coughing...?

my 3 month old son was around his older cousin last week who kept coughing, and now my son has been coughing the last few days and sounds pretty congested. i called the doctor who told me that he is too young for any medication but to put saline nasal spray in his nose a few times a day which doesnt really seem to be working. i feel bad because he wakes himself up by coughing and last night he coughed so hard that he threw up. :-( does anyone have any other advice that might work for him?